Some Bally Arcade/Astrocade Diagnostic Tips By Michael Matte June 7, 2020 Overview This document isn't a how-to or a FAQ: it's a document created based on information exchanged via a few emails, phone calls and pictures between Michael Matte, Adam Trionfo, Ken Lill and Allen Schweitzer in May/June 2020. Michael's final email response has some good information on troubleshooting the Astrocade. Some of this information might be a bit out of context without the original emails, yet I decided to ask Michael if I could post his information, as it might prove helpful to some people who are having issues with fixing their Astrocade consoles or just want a little background on some of the different revisions of the Bally Arcade/Astrocade motherboards. I hope that Michael's information will prove useful to Astrocade trouble-shooters. I've included Michael's original email in-full here. - Adam From: Michael Matte Sent: Sunday, June 7, 2020 1:55 PM To: Adam Trionfo Subject: Revised Follow Up To Allen Schweitzer I expanded a few comments to the original follow up to Allen. You can post either version. Thanks. This is my follow-up to your photo/info you emailed me on your four 2K ROM board and also when we teamed up over the phone to diagnose one of your failed motherboards. The following are comments/questions related (or not) to the above statement. I found a data sheet for the MK4096N-15 DRAM chip in Mostek's 1977 Memory Products Catalog. The maximum rating for the VDD supply voltage is 15.75V. The chip's access time is 350ns. In 1977, there were 12V 4096 chips and surprisingly 4027 chips available. No 4015 was listed in the catalog. I'm guessing, the –15 chip was used because it was the cheapest. The -15 chip was not listed in Mostek's 1979 data manual. I have 2 working motherboards with the white ROM package. Both of these boards utilize 4015N DRAM. One white ROM displays a 1977 menu and the other white ROM displays the 1978 menu. Any idea why the early motherboards utilized a plastic shield? Did the FCC later change the RF shield requirement to metal? The Bally schematic in the Bally Service Manual PA– 1 shows the 26 point (double-sided) and 10 point (double-sided) diagnostic test ports (plug-ins) using a diamond symbol, pin number and test port designation. An example is ◊ pin 23 (26) shown at pin 15 of U20. Thanks for sending me those photos of your four 2K ROM board. Do you have a close-up photo of the DRAM, the power supply and the front view of the +15V voltage regulator. If so, please email me them to complete my photo gallery of this rare motherboard. Thanks. You can reduce the size of your computer photos to just fit your own personal monitor by using Windows Paint Program. This will save you a bunch of memory bytes. You can also add text notes to your photos. My HP monitor resolution can only display up to 1600 x 900 pixels max. Even with my Canon camera set at 1920 x 1280 pixels (2.5M), I still reduce my photo size to just fit my monitor, which typically requires only under 500K bytes for a photo. I don't know how Windows reduces a hi-res camera photo to fit a monitor. Depending on the maximum pixel resolution your monitor can display, you might lose some fine detail in the Windows reduction. Whether there will be further loss of detail trimming down your camera photo using Windows Paint is unknown to me at this time. You could compare the normal Windows reduction with your Paint trimmed photo. Then decide if you really want to delete the actual hi-res camera photo file. Do those custom chips on your four 2K ROM motherboards have small square metallic heatsinks? Allen's photos of the custom chips on his early four 2K ROM motherboard reveal some very distinct artistic 40 pin packages. The 40 chip pins look goldplated. The top of the package depicts the physical internal wiring to the chip core. The square shaped labels on the top center of the packages had some depth to it. I thought it might be a small metallic heatsink. Allen said it is not a heatsink. The first test Balcheck performs is a RAM check, but this particular test only checks RAM locations 4F00-4FFFH (only 256 bytes) because the next check is for functioning screen interrupts, which requires a working Z80 stack area in RAM to execute a screen interrupt routine. Then Balcheck tests all of RAM. See the standard Balcheck tests in the BalcheckHR user manual for test details. All 4 ROMs on the motherboard are wired identically on the motherboard. Based on Ken's info related to the four 2K ROM internal addressed decoding, the memory allocation for each 2K ROM chip is indicated below. 8K ROM select 0000-1FFFH with chip internal address decoding Label A12 A11 HVSA 0 0 HVSC 0 1 HVSB 1 0 HVSD 1 1 HVSA U4 0000-07FFH HVSC U2 0800-0FFFH HVSB U3 1000-17FFH HVSD U1 1800-1FFFH Operating System 0000-0E18H 3 Games, Scribbling 0E19-1FFFH Motherboard Locations HVSD U1 HVSB U3 HVSC U2 HVSA U4 A BalcheckHR dual 7-segment display note. A lowercase b is used to represent the hex digit B. The lowercase b looks similar to the hex digit 6. Don't confuse b with 6 on the 7-segment display. A lowercase d is used to represent the hex digit D. The BalcheckHR user manual warns the user of this possible misread. BalcheckHR overlay The BalcheckHR user manual is written assuming an overlay is utilized. Buy and cut to size, some general-purpose stick on labels. Attach labels to the Scribbling or spare Astrobasic overlay and relabel. See the user manual for details. The Nutting Manual has some general info within its "System Description" which would likely help you diagnose a failed motherboard. There is also info in the BalcheckHR user manual related to troubleshooting. Both manuals are archived on the Bally Alley. SetScreen3 has an option to "Halt" the Z80 CPU, which might help your diagnosis when using a logic analyzer. When a Z80 Halts, it just executes NOPs. See SetScreen3 in the BalcheckHR user manual for details. There are also 2 troubleshooting loops. See the "Optional Troubleshooting Programs" in the BalcheckHR user manual. I did document a procedure for checking all 8 rectifier diodes for an "open" or "shorted" diode, without desoldering any diode leads. See my article in the Bally Alley FAQS section "Troubleshooting The Power Supply In The Bally/Astrocade Home Computer System". The procedure is described in the last paragraph of the section labeled "Full Wave Rectifiers", which begins on page 2. Next time you replace more than one RAM chip on a motherboard, please document any RAM error report before and after the chip replacement, plus the chip number that was replaced, so we can determine if any false reports were displayed. Thanks. I am likely going to write a commentary for the Balcheck RAM error report code 04. The commentary would cover topics such as listed below. What is Balcheck really telling me with the code 04 report? How does Balcheck test the 8 RAM chips? Is every RAM byte tested? How is a RAM error saved and reported? How are the screen RAM bits mapped? What exactly does each RAM chip store, screen bytes or pixel bits? Why does Balcheck sometimes display inconsistent or bad reports? End of follow-up Bye.